1. Field of the Invention
The present invention relates to an optical disc drive Compatible With a Plurality of Types of Optical Discs compatible with a plurality of types of optical discs of different track pitches to write and/or read data into and/or from a loaded one of such optical discs.
2. Description of Related Art
Compact discs (CD) as optical storage media are widely prevailing. The CD-type optical discs are used in various fields including musical applications. The compact discs for the musical applications are usually of the read-only type. Further, write-once type compact discs called CD-R have also been developed.
Further, optical discs called digital versatile disc/digital video disc have also been developed which are suitable for multimedia applications. They are proposed for many purposes such as storage of video data, audio data and computer data. Owing to the reduction of recording track pitch and data compression technology, the DVD has a remarkably increased capacity of recording though its size is the same as that of the CD (12 cm in diameter).
Optical discs of new different types have been and will possibly be developed more and more. In these situations, it is desired to provide an optical disc drive compatible with such newly developed types of CDs as well as conventional optical discs.
As far as the above-mentioned DVD is concerned, it is desired to develop an optical disc drive compatible with CD as well. To accommodate the differences in layer structure and other factors between CD and DVD, however, the optical disc drive for both CD and DVD should incorporate two pickups (or some elements of an optical system used in the pickup), one for CD and the other for DVD. Therefore, the dedicated pickups should be selectively used depending upon whichever is loaded in the optical drive, a CD or DVD.
In an optical disc drive in which such certain elements thereof are selectively used for the optical drive to be compatible with a plurality of different types of optical discs, it is necessary to accurately discriminate the type of an optical disc loaded in the optical drive.
In the case of a cartridge disc, namely, an optical disc housed in a cartridge, the type of an optical disc loaded in the optical disc drive can easily be judged by means of an ID hole or the like provided on the cartridge. However, a mechanical discriminating means like the ID hole cannot be adopted for discrimination of optical discs not encased in a cartridge and having a same size, like the above-mentioned CD and DVD.
Furthermore, use of sensors, and special parts intended for discrimination of the disc type is not desirable since they would add to the structural complexity and costs of manufacture of the optical drive products.
To meet the above-mentioned needs, the present invention has an object to provide an optical disc drive compatible with both an optical disc having a large track pitch and one of which the track pitch is small and adapted to accurately and simply discriminate the type of a loaded one of such optical discs.
The above object can be accomplished by providing an optical disc drive compatible with a plurality of types of optical discs of different track pitches to write and a read data into and/or from a loaded one of such optical discs, comprising a first pickup provided for a first optical disc having a first track pitch, a second pickup provided for a second optical disc having a second track pitch smaller than the first one, a focus servo circuit to control a focus servo of the first and second pickups and pull in the focus servo, based on a focus error signal, a tracking servo circuit to control tracking of the first and second pickups based on a tracking error signal and a control circuit to start pulling in the focus servo using the first pickup with respect to an optical disc loaded, detect, based on the focus error signal resulting from the focus servo pull-in operation such, that the first pickup is in a nearly perfect focus, move the first pickup radially relative to the disc when the first pickup is in the nearly perfect focus, and judge the loaded optical disc as the first one when a tracking error signal is detected during the radial move of the first pickup, or as the second one when no tracking error signal is detected during the radial move of the first pickup.
Furthermore, the above object can also be accomplished by providing an optical disc drive compatible with a plurality of types of optical discs having different recording densities to write and/or read data into and/or from a loaded one of such optical discs, comprising pickup means provided with a first light source to provide a laser beam of a first wavelength, and a second light source to provide a laser beam of a second wavelength shorter than the first one, and which radiates a laser beam from the first or second light source to an optical disc loaded in the optical disc drive, a servo processor for controlling focus and tracking servos of the pickup means based on an error signal and tracking signal and means for discriminating the type of a loaded optical disc based on the level of a tracking error signal included in a return component of the laser beam irradiated to the optical disc.
Further more, the above object can also be accomplished by providing a method of discriminating a plurality of optical discs of different track pitches, comprising the steps of moving an optical disc loaded in an optical disc drive in a direction toward and away from an objective lens, radiating a laser beam from a light source to a signal plane of the optical disc through the objective lens being moved, detecting a tracking error signal contained in the reflected beam from the signal plane and discriminating the type of the loaded optical disc based on the level of the detected tracking error signal.
The optical disc drive according to the present invention can discriminate, without actuation of the focus servo, an optical disc having a large track pitch from one having a small track pitch based on a tracking error signal detected when the pickup is present in the vicinity of the in-focus point. Thus, the optical disc drive according to the present invention can discriminate optical disc types one from another using no sensors, and special parts and others intended for detecting the type of an optical disc loaded in the drive.
Also, the optical disc drive according to the present invention can achieve a high speed of disc discrimination since only one pickup is used for the disc discrimination.
Furthermore, the optical disc drive according to the present invention can read and write, in a reduced time, data into and from a large track-pitch optical disc loaded in the drive since the CD focus loop can be pulled in while the disc type is being discriminated.